Sewing machine comprising a device for steering towards the end of a seam

ABSTRACT

A sewing machine has a device for steering towards a predetermined end (E) of a seam (B 1 ). An alternating movement of the feed elements of the sewing machine, which occurs when the stitch adjusting device is set, is taken into consideration in the calculation of the target stitch length (Sb) of the final optionally shortened end stitch (Nre) of the seam, in such a way that the setting value that deviates from the target stitch length is produced.

FIELD OF THE INVENTION

The present invention pertains to a sewing machine with a needle bardriven in an upwardly and downwardly movable manner with a needle feedmechanism, a feed dog and the needle driven oscillatingly in thedirection of feed, a stitch regulating device associated with the feedmechanism, and a device for controlling the sewing machine and forapproaching a predetermined end point of a seam at a spaced locationfrom the edge of a workpiece, the device comprises a sensor, which isarranged in front of the needle and triggers the operation forpositioning the needle at the seam end point during the passage of theworkpiece edge, the device has a pulse generator determining the speedof rotation and the angular position of a machine shaft and a computer,which controls the number of residual seam stitches and, via anadjusting device, the setting of the stitch regulating device forreaching the seam end point as a function of the distance between theneedle and the sensor and the angular position of the machine shaft,which is determined at the time of the edge recognition.

BACKGROUND OF THE INVENTION

A means for approaching the end point of a seam, in which this operationis triggered by means of a sensor scanning the passage of the workpieceedge extending at right angles or at an angle to the seam, is known fromDE 33 24 715 C2 (U.S. Pat. No. 4,528,923) in a sewing machine with lowerand needle feed. The means comprises, furthermore, a pulse generatordetecting the speed of rotation and the angular position of a machineshaft, by which the size of the partial stitch already pushed during theedge recognition is determined. The number of residual seam stitches,which are unchanged in length, and the length of the shortened endstitch or the length of a plurality of uniformly shortened residual seamstitches are calculated by means of a computer as a function of thedistance between the middle position of the needle of the sewing machineand the sensor, the seam distance and the length of the partial stitchyet to be pushed.

To adjust the stitch regulating device accurately and also comparativelyrapidly, the computer prompts the presetting of a stop for limiting themovement stop of a follower member coupled with the stitch regulatingdevice. This follower member is moved very rapidly against the stopbefore the beginning of the one shortened end stitch or of the first ofseveral shortened residual seam stitches by means of a compressed aircylinder and the stitch regulating device is thus adjusted to thedesired shortened stitch length.

It is expressly emphasized in the DE-C2 that the adjustment of thestitch regulating device takes place during the short time availableduring the phase of standstill between the needle and the workpiece.This should be understood to mean that the exact adjustment of thestitch regulating device can take place only in the middle of the phaseof feed of the feed dog and the needle and consequently with the lowerneedle feed.

The same situation that was described in the specification of the DE-C2concerning the sewing unit for sewing calender envelopes of the firm ofAdler would otherwise occur. A sewing machine with lower feed is used inthis prior-art sewing unit. When the stitch regulating device is set tothe stitch length zero in this unit during the feed motion in order tointerrupt the feed motion of the workpiece as a result, this can beperformed with sufficient accuracy only if the feed dog has performedexactly half of its feed motion during the adjustment of the stitchregulating device and is therefore in the middle of the needle. Becauseof the existing kinematics of stitch regulating devices, the feed dogalways assumes the middle position during the adjustment of the stitchregulating device to zero. If the adjustment of the stitch regulatingdevice is performed before or after the middle position of the feed dog,the latter will therefore perform a forwardly or backwardly directedoffset movement toward the middle of the needle. Since this happenswhile a feed step is being performed, during which the feed dog is incontact with the workpiece, the workpiece also performs the offsetmovement of the feed dog, and this movement is therefore also calledpushing movement.

Such an offset movement also occurs in the sewing machine with lower andneedle feed known from the above-mentioned DE 33 24 715 C2 during theadjustment of the stitch regulating device. The effects of this on thestitch length of the sewing stitch to be performed thereafter areillustrated in the drawing on the basis of the movement of the needle,whose tip describes elliptical movement paths.

FIG. 4 shows the movement path of the needle 5 during a feed cycle,during which the stitch regulating device is set to the stitch length Sand the needle 5 feeds the workpiece W together with the feed dog 9 bythe amount of the set stitch length S in the direction of feed V. Themovement path of the needle 5 is now symmetrical to the middle of theneedle Nm.

FIG. 5 shows the situation that would occur if the stitch length Sb of aresidual seam end stitch located at the end point of the seam weredetected by means of the computer after an edge recognition and thestitch regulating device were set to the stitch length Sb during thereturn phase of the needle and the feed dog. After the completion of thelast feed cycle, the last point of insertion of the needle 5 or thepoint at which the needle exits is located at a distance S/2 in thedirection of feed V behind the middle of the needle Nm. If the stitchregulating device is set to the lower value Sb, the needle bar firstperforms an offset movement in the direction of the middle of the needlebecause of the above-mentioned existing kinematics of stitch regulatingdevices. The needle bar then moves in front of the middle of the needleNm by the amount Sb/2 when viewed in the direction of feed V. A stitchlength of Sz=S/2+Sb/2 is thus obtained for the next sewing stitch. If,e.g., the stitch length is S=4 mm and a stitch length of Sb=1 mm wascalculated for the residual seam end stitch, a stitch length ofSz=4/2+1/2=2.5 mm would be obtained for the last stitch. The last stitchwould thus be too long by 1.5 mm.

To avoid such an offset movement leading to an unusable result, theadjusting movement of the stitch regulating device must be, as wasmentioned, very rapid, i.e., sudden in the middle of the feed phase.However, the consequence of this is that the adjustment operation causesa vibration of the sewing machine and a corresponding noise. If, bycontrast, the adjustment operation shall take place more slowly, thesewing machine would have to be briefly stopped for this purpose, whichwould interrupt the sewing operation and lead to a loss of time.

These problems are avoided in the means known from DE 33 42 391 C1 (U.S.Pat. No. 4,587,915) such that the setting of the stitch regulatingdevice remains unchanged in this means for the performance of a singleshortened end stitch or a plurality of shortened residual seam stitches,and the feed dog is raised, instead, during its return phase, whichnormally takes place in the lowered position, until it pushes theworkpiece back against the normal direction of feed by the amount bywhich the next end stitch or residual seam stitch shall be shortened.Aside from the fact that this means is technically highly complicated,another drawback lies in the fact that it may sometimes lead toinaccurate results because the feed dog, which now acts as the only feedmeans, is operating against the normal direction of feed of its teethduring the reverse push, and a slip, whose amount depends very stronglyon the properties of the particular fabric of the workpiece, maytherefore develop between the feed dog and the workpiece.

SUMMARY OF THE INVENTION

The basic object of the present invention is to provide a sewing machinewith a means for approaching a predetermined end point of a seam, whichhas a simple design and in which the adjustment of the stitch regulatingdevice can be carried out without interruption of the sewing operation.

The present invention is based essentially on the idea of adjusting thestitch regulating device during the phase of return of the feed meansbefore the sewing of a shortened end stitch or residual seam stitch suchthat the offset path of the feed means, which thus arises, is also takeninto account, so that the end stitch of the seam is carried out with thenecessary stitch length and the seam is terminated precisely at thepoint predetermined by the amount of the particular seam distance.

The process is also suitable for sewing uniformly shortened residualseam stitches. However, the particular offset path, which isconsequently the current offset path, must be taken into account in thiscase for sewing every individual residual seam stitch, and the stitchregulating device must be set separately for every individual residualseam stitch.

The law that is equally applicable to both types of seam end management,by which the amount of the offset path is taken into account withouthaving to determine it directly, is described.

The adjusting device for the stitch regulating device is formed by astepping motor. This design of the adjusting means, which is simplecompared with the state of the art, is made possible by the fact that bytaking into account the offset path of the feed means, which arisesduring the adjustment of the stitch regulating device, the adjustmentoperation does not need to take place abruptly, but it can be performedduring the comparatively long time of the return phase of the feedmeans.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a view of a sewing machine with a schematic block diagram ofthe control means;

FIG. 2 is a schematic view of a seam section with a shortened residualseam end stitch;

FIG. 3 is a schematic view of a seam section with a plurality ofuniformly shortened residual seam stitches;

FIG. 4 is the movement path of the needle during the performance of afeed cycle;

FIG. 5 is the movement path of the needle after the adjustment of thestitch regulating device with the effect of the offset movementoccurring during the adjustment; and

FIG. 6 is the movement path of the needle after the adjustment of thestitch regulating device with the compensation of the offset movement,which compensation is performed in the process.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in particular, in the sewing machine 1, thebase plate is designated by 2 and the upper housing by 3. A needle bar4, which can be moved up and down, is arranged with a needle 5 in thehead of the upper housing 3. A hook shuttle, not shown, cooperates withthe needle 5 in the known manner.

The feed mechanism 6 of the sewing machine 1 is designed as a lower andneedle feed, as in the sewing machine according to DE 33 24 715 C2mentioned in the introduction, and it therefore comprises a feed dog 7arranged in the base plate 2 and the needle 5. The needle bar 4 isaccommodated for this purpose in the known manner in a needle barpendulum, which is not shown in the drawings. The feed dog 7 and theneedle bar pendulum are connected to a drive mechanism, which ispartially coupled with one another, and which corresponds to the drivemechanism disclosed in the DE-C2 and therefore will not be shown anddescribed here once again.

A common stitch regulating device 8 is used to set the amount of feed ofthe feed mechanism 6. It has a first adjusting mechanism 9 shownschematically in FIG. 1 for the feed dog 7, and this mechanism 9corresponds to the adjusting mechanism 26 in the above-mentioned DE-C2.The stitch regulating device 8 has a second adjusting mechanism, notshown, for the needle 5, which comparably corresponds to the adjustingmechanism 44 in the DE-C2.

An adjusting shaft 10, which is connected to the adjusting shaft of thesecond adjusting mechanism in the usual manner via coupling members, isassociated with the adjusting mechanism 9, so that the two adjustingmechanisms always have the same setting value and are always set to thesame stitch length. The adjusting shaft 10 is connected to a steppingmotor 11. Due to the two adjusting mechanisms being coupled, thestepping motor 11 is used for both and there is, on the whole, a commonadjusting means for the stitch regulating device 8.

A positioning motor 12 arranged in the base plate 2 with a control 13 isused to drive the sewing machine 1. The positioning motor 12 drives,among other things a drive shaft 14 for the feed dog 7 in a manner notshown more specifically. A pulse generator 15 is arranged at thepositioning motor 12, the pulse generator 15 being used to determine thespeed of rotation of the sewing machine 1 and the angular position ofthe drive shaft 14 when an edge K2 of a workpiece W passes through thelight beam of a photoelectric cell, of which only a sensor 16 arrangedat the head of the upper housing 3 is shown.

A control means 17, which contains a computer 18, is associated with thesewing machine 1. The computer 18 comprises essentially a processor 19,an I/O member 20 and at least one EPROM 21. The control means 17contains, furthermore, an operating element 22 connected to the computer18.

The mode of operation is as follows:

The scanning point A of the sensor 16 is located at a distance L fromthe middle position M of the needle 5. During the preparation of a seamB1 consisting of sewing stitches N of a stitch length S at a distance afrom the edge K1 of a workpiece W, the sensor 16 reports the passage ofthe edge K2 of the workpiece W through the scanning point A.

The size Sa of the partial stitch not yet completed at the time of therecognition of the edge, which is to be taken into account subsequentlyduring the residual seam extending over the length 1, is determined bymeans of the computer 18 in the same manner as described in theabove-mentioned DE 33 24 715 C2.

In the case of the manner of seam end management shown in FIG. 2, inwhich the partial stitch yet to be pushed is taken into account onlyduring the residual seam stitch NRe, the number of residual seamstitches NR to be formed with unchanged stitch length S and the lengthSb of the residual seam end stitch NRe are now calculated by thecomputer 18 as a function of the residual seam length 1 and the stitchlength S set originally.

The length Sb of the residual seam end stitch NRe now forms the desiredstitch length necessary for ending the seam B1 exactly at point E. Tocompensate the offset path of the feed dog 7 and the needle 5, whicharises during the adjustment of the stitch regulating device 8, thecomputer 18 calculates from this, moreover, the value Sen to be actuallyset according to the formula

Sen=2×Sb−Sea.

Here,

Sen=new stitch length to be set

Sb=necessary desired stitch length for the residual seam end stitch NRe

Sea=old stitch length set; this corresponds to the original stitchlength S in this seam end variant.

Calculation Example:

S=Sea=4 mm

Sb=1 mm

Sen=2×1 mm −4=−2 mm.

This means that the stitch regulating device 8 must be set to the value−2 mm, i.e., to a reverse stitch of 2 mm, by means of the stepping motor11 during the return phase of the feed means 5, 7. If this has thushappened, the feed mechanism 6 performs a forwardly directed feed motionover a length of 1 mm to form the residual seam end stitch NRe, as itcorresponds to the necessary desired stitch length Sb.

FIG. 6 shows this situation on the basis of the movement path of theneedle 5. After completion of the feed cycle of the last residual seamstitch NR with the stitch length S=4, the point at which the needleexits is located at a distance of S/2=2 mm behind the middle of theneedle Nm. If the stitch length Sen=−2 mm is set, the needle bar 4remains in the area behind the middle of the needle Nm because of thereverse feed to be set, and a new point of insertion, which is located−2/2=−1 mm behind the middle of the needle, arises for the needle 5. Itfollows from this that the residual seam end stitch NRe is indeed formedwith a stitch length of 1 mm.

The offset movement of the feed dog 7 and the needle 5, which arisesduring the adjustment of the stitch regulating device 8 taking placeduring the return phase of the feed dog 7 and of the needle 5, is thuscompensated. If this compensation of the offset movement did not takeplace and the stitch regulating device 8 were set at the value of thedesired stitch length of 1 mm, an effective stitch length of 2.5 mmwould be obtained for the residual seam end stitch NRe, as is shown inFIG. 5, as a consequence of which the actual end point of the seam wouldbe beyond the desired end point E by 1.5 mm.

If the first sewing stitch of the second seam B2 along the workpieceedge K2 is to have the same length as the residual seam end stitch NReto obtain a symmetrical design of a seam corner area, the stitchregulating device 8 must be set to the value

Sen=2×Sb−Sea

=2×1 mm−(−2 mm)

=4 mm.

This value corresponds to the normal stitch length S. Consequently,while the first sewing stitch of the second seam has reached the desiredlength of 1 mm, the second sewing stitch and all further sewing stitchesare formed with the normal stitch length 4 mm while the setting of thestitch regulating device 8 now remains unchanged.

To perform the type of seam end management shown in FIG. 3, in which thepartial stitch yet to be pushed is taken into account in the case of,e.g., three uniformly adapted residual seam stitches NRv, the computer18 now calculates the number of residual seam stitches NR to be formedwith unchanged stitch length S and the length Sc of the three shortenedresidual seam stitches NRv as a function of the residual stitch length 1and the stitch length S set originally.

The length Sc of the residual seam stitches NRv forms here the desiredstitch length of the last three residual seam stitches NRv that isnecessary for ending the seam B1 exactly at point E. To compensate theoffset path of the feed dog 7 and of the needle 5, which arises duringthe adjustment of the stitch regulating device 8, the computer 18calculates, moreover, the value Sen to be actually set for everyindividual of the last three residual seam stitches NRv, doing soaccording to the formula

Sen=2×Sc−Sea.

This formula corresponds exactly in terms of its contents to theabove-mentioned formula. The only difference is that the desired stitchlength of the last three residual seam stitches NRv is called Sc in thisformula, whereas the desired stitch length of the only residual seamstitch NRe was called Sb in the first-mentioned formula.

Calculation Example:

S=4 mm

Sc=3 mm.

First Shortened Residual Seam Stitch NRv

Sen=2 ×3 mm−44 mm=2 mm

The original stitch length S=4 is to be used here for Sea.

Second Shortened Residual Seam Stitch NRv

Sen=2×3 mm−2 mm=4 mm

The stitch length Sen=2 mm set before is to be used here for Sea.

Third Shortened Residual Seam Stitch NRv

Sen=2×3 mm −4 mm=2 mm

The stitch length Sen=4 mm set before is to be used here for Sea.

It follows from this that the stitch regulating device 8 must be setseparately for every individual residual seam stitch NRv for sewing aplurality of uniformly shortened residual seam stitches NRv in order tocompensate the current offset path occurring in the particular case.

If the starting area of the second seam B2 shall look like the end areaof the first seam B1 with this type of seam end management, and thisseam therefore begins with three shortened sewing stitches of a lengthof 3 mm each, and the sewing of this seam is then to be continued with astitch length of 4 mm, the stitch regulating device 8 must be set to thevalue Sen=4 mm for the first sewing stitch, to the value Sen=2 mm forthe second sewing stitch and to the value Sen=4 mm for the third sewingstitch. Sewing can then be continued with the last setting value,because this value corresponds to the normal stitch length S=4 mm.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. A sewing machine comprising: a needle bar drivenin an upwardly and downwardly movable manner with a needle; a feedmechanism with a feed dog and with said needle driven oscillatingly in adirection of feed; a stitch regulating device associated with said feedmechanism; control means for controlling the sewing machine and forapproaching a predetermined end point of a seam at a spaced locationfrom an edge of a workpiece W, said control means including a sensorarranged in front of said needle and triggering an operation forpositioning said needle at a seam end point during the passage of aworkpiece edge, a pulse generator determining the speed of rotation andthe angular position of a machine shaft and a computer controlling anumber of residual seam stitches and, via an adjusting device, thesetting of said stitch regulating device for reaching said seam endpoint as a function of the distance between said needle and said sensorand the angular position of said machine shaft is determined at the timeof the edge recognition and to obtain a desired stitch length of aresidual seam end stitch, which is adapted in terms of length, saidstitch regulating device is adjustable between the end of a feed phaseof the preceding, yet unchanged residual seam stitch and the beginningof the feed phase of the residual seam end stitch, taking into accountthe current offset path of said feed dog and said needle, which arisesduring the adjustment of said stitch regulating device.
 2. A sewingmachine comprising: a needle bar driven in an upwardly and downwardlymovable manner with a needle; a feed mechanism with a feed dog and withsaid needle driven oscillatingly in a direction of feed; a stitchregulating device associated with said feed mechanism; control means forcontrolling the sewing machine and for approaching a predetermined endpoint of a seam at a spaced location from an edge of a workpiece W, saidcontrol means including a sensor arranged in front of said needle andtriggering an operation for positioning said needle at a seam end pointduring the passage of a workpiece edge, a pulse generator determiningthe speed of rotation and the angular position of a machine shaft and acomputer controlling a number of residual seam stitches and, via anadjusting device, the setting of said stitch regulating device forreaching said seam end point as a function of the distance between saidneedle and said sensor and the angular position of said machine shaft isdetermined at the time of the edge recognition and to obtain the desiredstitch length of a plurality of residual seam stitches, which areadapted in terms of length, said stitch regulating device is adjustablefor every individual of said residual seam stitches to be adaptedbetween an end of a feed phase of said preceding residual seam stitchand the beginning of the feed phase of a subsequent residual seamstitch, taking into account the current offset path of said feed dog andsaid needle, which arises during the adjustment of said stitchregulating device.
 3. A sewing machine in accordance with claim 1,wherein the adjustment of said stitch regulating device, which is to beperformed to form said residual seam end stitch adapted in terms oflength or said residual seam stitches adapted in terms of length, isperformed according to the following relationship: new stitch length tobe set is equal to two times the desired stitch length or the desiredstitch length less the old stitch length set for the preceding sewingstitch.
 4. A sewing machine in accordance with claim 1, wherein theadjusting means is formed by a stepping motor.
 5. A sewing machine inaccordance with claim 2, wherein the adjustment of said stitchregulating device, which is to be performed to form said residual seamend stitch adapted in terms of length or said residual seam stitchesadapted in terms of length, is performed according to the followingrelationship: new stitch length to be set is equal to two times thedesired stitch length or the desired stitch length less the old stitchlength set for the preceding sewing stitch.
 6. A sewing machinecomprising: a needle bar driven in an upwardly and downwardly movablemanner with a needle; a feed mechanism with a feed dog and with saidneedle driven oscillatingly in a direction of feed; a stitch regulatingdevice associated with said feed mechanism; control means forcontrolling the sewing machine and for approaching a predetermined endpoint of a seam at a spaced location from an edge of a workpiece W, saidcontrol means including a sensor arranged in front of said needle andtriggering an operation for positioning said needle at a seam end pointduring the passage of a workpiece edge, a pulse generator determiningthe speed of rotation and the angular position of a machine shaft and acomputer controlling a number of residual seam stitches and, via anadjusting device, the setting of said stitch regulating device forreaching said seam end point as a function of the distance between saidneedle and said sensor and the angular position of said machine shaft isdetermined at the time of the edge recognition and one of: to obtain thedesired stitch length (Sb) of a residual seam end stitch (NRe), which isadapted in terms of length, said stitch regulating device is adjustablebetween an end of a feed phase of the preceding, yet unchanged residualseam stitch (NR) and the beginning of the feed phase of the residualseam end stitch (NRe), taking into account the current offset path ofsaid feed dog and said needle, which arises during the adjustment ofsaid stitch regulating device, and to obtain a desired stitch length(Sc) of a plurality of said residual seam stitches (NRv), which areadapted in terms of length, said stitch regulating device is adjustablefor every individual of said residual seam stitches (NRv) to be adaptedbetween the end of the feed phase of the said preceding residual seamstitch NR or NRv and the beginning of the feed phase of the saidsubsequent residual seam stitch NRv, taking into account the currentoffset path of said feed dog and said needle, which arises during theadjustment of said stitch regulating device.